This invention relates to a fluorescent lamp and, more particularly, to a fluorescent lamp used in place of an incandescent lamp for saving electric power.
Fluorescent lamps are widely used for their excellent luminous efficacy and low power requirement. However, since fluorescent lamps are of generally straight or annular shape, they cannot be directly coupled to receptacles with screw bases of incandescent lamps. Recently, fluorescent lamps replaceable with the incandescent lamps are being developed for this reason. In a fluorescent lamp of this type, a reactance ballast and a starter circuit are assembled in an envelope with a base of the same type as that of an incandescent lamp (e.g., Type E-26); this fluorescent lamp is turned on as it is screwed into a receptacle which is normally used for an incandescent lamp.
However, with such a conventional fluorescent lamp, since the fluorescent tube and the reactance ballast are encased inside a globe member, the air inside the globe member is heated by the energized fluorescent tube and the operated reactance ballast. When the fluorescent tube is illuminated for an extended period of time in air at such a high ambient temperature, the mercury vapor pressure of the fluorescent tube exceeds the optimal vapor pressure. As a result, the intensity of ultraviolet rays inside the fluorescent tube and the luminance of visible light rays emitted from the fluorescent material coated on the inner surface of the fluorescent tube decrease considerably, disadvantageously degrading the luminous efficacy of the fluorescent lamp.
Further, when the temperature inside the globe member is raised, the current flowing through the fluorescent lamp increases with this temperature increase, resulting in generation of heat by the reactance ballast. The heat generated by the reactance ballast raises the temperature inside the globe member and degrades the luminous efficacy of the fluorescent tube. In the worst case, the reactance ballast may burn out completely.
It is, therefore, an object of this invention to provide a fluorescent lamp wherein the ambient temperature of the fluorescent tube encased in the envelope is not raised so much as to adversely affect the fluorescent tube.
In accordance with this invention, a fluorescent tube with bend parts is encased in an envelope with a screw base. A reactance ballast for regulating the current to flow through the fluorescent tube is fixed to a supporting plate which is attached to the fluorescent tube. Openings are formed in the envelope for expelling heat generated inside the envelope while the fluorescent tube is lit.